The fracturing technologies and fracturing fluids have experienced more than 60 years' development since the United States carried out the first work of fracturing stimulating production in 1947. The water-based fracturing fluids have occupied a dominant position because this technology develops fastest and the system has comprehensive advantages. Among the water-based fracturing fluids, the guar system occupies 70-90% of market share because of its performance advantages. Fracturing has been rapidly developed and widely applied as the major method for increasing production and increasing injection of the oil and gas reservoir. The fracturing fluid is one of the important parts of the fracturing technologies. At present, the common fracturing fluids are major polymer hydrogel fracturing fluids crosslinked by boron, zirconium, titanium, etc. These fracturing fluids mainly use their viscose properties to carry sand. Consequently the fracturing fluids have high initial viscosity, high thickener concentration, large construction friction resistance and poor temperature-resistance performance, poor sand-carrying performance at high temperature. The sand-carrying property needs further improvement. At the same time, the used crosslinking agent will finally return to the ground together with flowback fluid in the form of ions containing the crosslinking agent. And therefore, the used crosslinking agent requires post-treatment.
90% of global guar gum is from India and Pakistan. It has high risk on supply security. The guar gum was up to 180,000 Yuan per ton in 2012. The high price of guar gum not only increases the fracturing cost of the oil reservoir, but also causes huge pressure for normal fracturing production.
Some scholars have tried to use epichlorohydrin as the crosslinking agent to prepare the crosslinked guar gum or derivatives thereof. The relatively high degree of crosslinking is achieved, but the solubility of the prepared crosslinked guar gum is not high in water, and thus is not suitable in field of fracturing fluids (Tang Hongbo, Wang Xiguang, Li Yanping, Preparation of cross-linked guar gum, Food science, 2012, Vol. 33, No. 16: 72-76; Chen Nali, Feng Huixia, Zhao Xia, et al, Study on preparation of crosslinked carboxymethyl guar gum, Science and technology of food industry, 2011, 10: 292-294).
Hydraulic fracturing technology needs to consume large amount of water resource. In districts where the supply demand is high relative to the available water resource, the water extraction made by the well drilling and hydraulic fracturing operations may cause increasingly serious problems of water resource depletion and environmental degradation. These operations, including the fracturing work on the offshore working platform, need to deliver fresh water to the working platform. Therefore, whether in the view of operation cost or in the view of environmental protection, the recycling use technology of fracturing flowback fluid has become the trend of the fracturing technology for using water resource effectively and reasonably.